gossip: Gossip error messages
gossip: Gossip error messages

We are printing out error messages when a remote connection is closed

   ERROR   [shard 0] gossip - Fail to send GossipDigestACK2 to 127.0.0.2:0: rpc::closed_error (connection is closed)
   ERROR   [shard 0] gossip - Fail to handle GOSSIP_DIGEST_ACK: rpc::closed_error (connection is closed)
   WARN    [shard 0] unimplemented

this is causing issues with DTEST as it validates after finishing a run
that there are no ERRORs in the log

The rule is:
   We can handle it correctly if error occurs -> log warn
   We can not handle it correctly when error occurs -> log error

Fixes #144

wildinto/scylla,stamhe/scylla,rentongzhang/scylla,duarten/scylla,scylladb/scylla,dwdm/scylla,glommer/scylla,glommer/scylla,rluta/scylla,eklitzke/scylla,senseb/scylla,rentongzhang/scylla,bowlofstew/scylla,phonkee/scylla,tempbottle/scylla,respu/scylla,shaunstanislaus/scylla,respu/scylla,stamhe/scylla,justintung/scylla,raphaelsc/scylla,kangkot/scylla,rluta/scylla,capturePointer/scylla,capturePointer/scylla,linearregression/scylla,aruanruan/scylla,respu/scylla,aruanruan/scylla,justintung/scylla,tempbottle/scylla,aruanruan/scylla,bowlofstew/scylla,eklitzke/scylla,kjniemi/scylla,asias/scylla,stamhe/scylla,duarten/scylla,avikivity/scylla,acbellini/scylla,eklitzke/scylla,duarten/scylla,kangkot/scylla,victorbriz/scylla,acbellini/scylla,avikivity/scylla,wildinto/scylla,asias/scylla,capturePointer/scylla,gwicke/scylla,shaunstanislaus/scylla,kjniemi/scylla,dwdm/scylla,rluta/scylla,acbellini/scylla,senseb/scylla,wildinto/scylla,linearregression/scylla,linearregression/scylla,raphaelsc/scylla,guiquanz/scylla,scylladb/scylla,gwicke/scylla,raphaelsc/scylla,scylladb/scylla,phonkee/scylla,asias/scylla,guiquanz/scylla,senseb/scylla,phonkee/scylla,guiquanz/scylla,tempbottle/scylla,scylladb/scylla,bowlofstew/scylla,gwicke/scylla,kangkot/scylla,dwdm/scylla,justintung/scylla,avikivity/scylla,glommer/scylla,kjniemi/scylla,rentongzhang/scylla,victorbriz/scylla,shaunstanislaus/scylla,victorbriz/scylla